Infrared photography has shown that a great deal of information about most common scenes can be obtained in the longer wavelength regions which fall outside of visible range. However, such photography has serious limitations. Observable photon wavelengths are limited to less than one micrometer making much of the potential information in the scene unavailable. Also, such systems have no real-time capability, a necessity for many military and civilian tactical uses.
To overcome these limitations photon sensitive diodes and photoconductors have been developed which are sensitive to photons of wavelength greater than one micrometer. Because of the relatively fast response time of these detectors, both to light-on and light-off conditions, they have been incorporated into realtime systems. The disadvantage of these systems has been their requirement for mirrors to scan the field of view. This requirement adds to the weight and power requirements of the final system, in addition to degrading the mechanical ruggedness of the system.
The next generation of infrared viewing systems foresees the elimination of these mechanical scan mirrors. This will require a high density of infrared sensitive detectors over a relatively large area (approximately 1 inch squared). Such detectors, if photoconductive, must have a high resistivity in the direction of the plane on which they are deposited if adequate frame storage times are to be achieved. Presently, the lead salt detectors, if formed by repeated depositions, can exhibit a high resistivity perpendicular to the plane on which they are deposited. The problem of increasing their resistivity in the direction of the plane on which they are deposited is addressed by this invention.